Dynamic braking of a single directcurrent series motor



N 13, 1951 .1. D. LEITCH ET AL 2,575,021

DYNAMIC BRAKING OF A SINGLE DIRECT CURRENT SERIES MOTOR Filed March 21,1947 3 Sheets-Sheet 1 Z] ZZ- lZa b h? Ilia ma A9 a U0 Q0 wv jib Ma 01,lZb /9 /5 b /8' /8b /6 I I gm;

INVENTORJ JOHN D. LE/TCH AND 7/) 1/1. a. WH/TE- BY mv fwv fO/ZME Y6 Nov.13, 1951 J. D. LEITCH ET AL DYNAMIC BRAKING OF A SINGLE DIRECT CURRENTSERIES MOTOR 3 Shets-Sheet 2 Filed March 21, 1947 INVENTORJ 3 3 2 M hm WI; L A w H m Nov. 13, 1951 J. D. LEITCH ET AL DYNAMIC BRAKING OF ASINGLE DIRECT CURRENT SERIES MOTOR 3 Sheets-Sheet 5 Filed March 21, 1947INVENTORS JOHN Dv LE/TCH AND BY PAUL. G. WH/Tfi.

Patented Nov. 13, 1951 DYNAMIC BRAKING OF A SINGLE DIRECT- CURRENTSERIES MOTOR John D. Leitch, Shaker Heights, and Paul G.

White, Cleveland, Ohio, assignors to The Electric Controller & Mfg. 00.,Cleveland, Ohio, a

corporation of Ohio Application March 21, 1947, Serial No. 736,146

20 Claims.

This invention relates to a control system for a direct current motor,and more particularly to a control system which connects the armaturewinding and the series field winding of a reversible motor automaticallyin the proper relationship in a loop circuit for dynamic brakingregardless of the direction of the motor rotation and which also reducesautomaticall the resistance of the loop circuit as the motordecelcrates.

A switching means of the reversing type is often used to completeselectively dynamic braking loops for a reversible series motor in orderthat the current in the armature winding but not in the field windingreverses when braking operation is desired. This selective currentreversalinsures that braking torque is obtained regardless of thedirection of motor rotation. For many applications it is desirable thatthe braking switching means comprise a pair of forward braking contactsand a pair of reverse braking contacts all normally biased to theirclosed positions. During normal running of the motor all of the brakingcontacts are held open against their bias. either by choice of theoperator or for other reasons, the motor is disconnected from the sourceand a selected pair of the braking contacts is permitted to close. Whichpair of the braking contacts is selected for closure depends upon thedirection of motor rotation.

For automatic operation it is desirable that the braking switching meansbe responsive to the actual direction of rotation of the motor in orderto avoid closure of the incorrect pair of braking contacts under alloperating conditions. Previous known systems using mechanicaldirectionally responsive switches or counter-E. M. F. relays forcontrolling the braking switching means by means of mechanicalinterlocks have not been completely satisfactory. Mechanicaldirectionally responsive switches associated with the motor shaft aredifiicult to install and maintain and the counter-E. M. F. relays andtheir associated circuits when used to control the operation of thebraking switching means are subject to the possibility of failure. Themechani cal interlocks are also subject to failure and are inherentlycomplicated anad difficult to adjust properly.

For controlling the dynamic braking action as the motor decelerates, itis desirable that means be provided to reduce the resistance of thedynamic braking loop at least once during the stopping operation. It isalso desirable that the When braking is desired, L

2 operator be able to select relatively strong or relatively weakbraking under normal operating conditions and that only relativelystrong braking be obtained upon failure of power.

It is an object of this invention to provide an improved control systemfor dynamically braking a direct current motor.

Another object is to provide a control system for dynamically braking areversible series motor which control system does not have the foregoindisadvantages.

Other objects are to provide a dynamic braking control system in whichthe switching means for completing the dynamic braking circuits iscontrolled in an improved manner by the counter- E. M. F. of the motor;to provide a dynamic braking control system in which normally closedcontactors for completing the dynamic brakin circuits are selectivelycontrolled directly by the counter-E. M. F. of the motor; to provide adynamic braking control system in which the pair of a group of fourcontacts which is to close to complete a dynamic braking loop isselected by means of the directional relationship of fluxes in themagnetic circuit of the contact operating means prior to braking; toprovide an improved dynamic braking control system for braking a seriesmotor automatically upon failure of power from either direction ofrotation; and to provide improved means for graduating automatically thedynamic braking action of a direct current motor.

In accordance with this invention, a forward pair and a reverse pair ofnormally closed dynamic braking contacts are held open magneticallyduring normal running operation of the motor by respective fluxesproduced by windings energized from the supply source for the motor. Ifthe motor is operating in the forward direction, the magnetic fluxholding open the reverse pair of braking contacts is augmented by amagnetic flux produced by a winding energized by the voltage drop acrossthe motor armature, and the magnetic flux holding open the forwardbraking contacts is opposed by and consequently reduced by a magneticflux produced by a winding also energized by the voltage drop across themotor. Upon failure of power or action of theoperator, the motorarmature is disconnected from the source and the magnetic fluxes of thewindings energized from the supply source and normally tending to holdall of the braking contacts open are reduced to zero. Thereupon, theforward pair of braking contacts closes since the resultant flux holdingthat pair of contacts open must reduce tinues to rotate due to theaction of the flux produced by the winding associatediwith. those"-contacts and energized by theyoltage dropacrosa the armature. Since thedirection oftheuvoltagei' drop across the armature depends upon thedirection of motor rotation, the-assisting and opposing action of themagnetic fluxes is reversed" with respect to the two pairs ofcontactsiroin that just described if the motor is operating in9;-16V8IS8 direction."

Two separate portions or the dynamic brakingresistor are arranged to beby-passedbytwononmally closed contacts respectively, which, dur-e ingoperation? ofthe 1 motor; are held:v open magneticallyi Braking. maybeeilectedby actionofthe operator with both resistance shuntingrconetacts-pen substantially throughout the braking cycle-on with: thecontacts closing.- iii-delayedsequence during,v braking as desired. Themotor speed' at which the second contact closesisselected-by controllingthe resistance. oi the energizing, circuitof. the winding'operatingtheses- 0ndv contact; Uponxfailure. of power one of theresistance shunting contacts-closes; but the-other. resistanceshuntingcontact is heldopen by the voltage drop across the.armatureuntil a predetermined reduced motor speed is reached. That oneof the resistance shunting contactsis definitely. open at the start of:braking insures that adequate brakingresistance. effective in. the.

braking loop at the timewhen. the. counteris highest. and. permits theresistance value-oi the portionof the-dynamic braking resister not.by-passedlby the contacts. to be chosen withoutiregard to. the pick-upvalue of devices. responsive to the lor'akingcurrentl.

Other objects and advantages. will become apparent from the followingdescription of the invention' wherein. reference is made to. thedrawings; in which:

Fig. 1 is a wiring diagram showing the directionaLbraking control;

Figs. ZLand'L 3 are wiring diagrams showing connections. for forward".running. and. braking after forward. running, respectively;

. Figs,.4fland: arewirihg diagram showingc'on-r Iiections. for. reverse;running and braking. after reverse running, respectively;

6 isa wiring.diagramshowingcontrollfor. graduating'the braking torque;and

Fig.7 is a wiring'diagram of acomplete motor controller;

Many. of the contactors and'relays are shown incompletelyifi Figs. 1 to6, but all of the con- Eater and" relays are shown completely inReferring to the drawings, adirectionallyre'sponsive; graduatedLdynamic. braking, control system inaccor'dance with this invention isshown for a series motor having an armature. winding land a' seriesfieldwinding II'. The opposing v terminals of the armature are indicatedat Illa and" Illbjand the opposing terminals of the field windingare'indicated at Iiaa'nd Ill). The pornon of the system shown in Fig. 1includes a 300; at low speeds of themotor; the windings IGp pair offorward running contacts I2a and I2b, a pair of reverse running contactsIda and Nb, a negative line contact I5a, a pair of forward brakingcontacts Isa and [6b, a pair of reverse braking contacts I80, andl8b,.a.suitable. acceleration, plugging, and speed control means I9 tobe later described, and a dynamic braking resistor 20. The contacts 12a,I2b, Ma, Nb, and 15a may be operated in any suitable manner, butpreferably are electromagnetically-"o'perated. As hereinafterdescribed'with: reference to Fig. '7, the contacts I2a and 1211 arenormally open contacts of an electro- 'magnetic. contactorr I'2', thecontacts Ma and Nb are-normally openicontacts of an electromagneticcontactor I4, andzthe contact I5a is a normally open contact of anelectromagnetic contactor I5.

Theron'tacts new and Ifib are normally biased to their. closed positionsillustrated in Fig. 1 as by a spring (not ShOWIUE'Ol gravity, and aremain contacts. of anelectromagnetic forward braking contactor. I 6having an operating vwihdir'igi. I610; a. polarizing winding Hip, and" anormany. open; control circuit contacti I60. Eikewis'e', the? con"-tacts I821. and. 181) are. normally biased to: their closed. positionsand are main contacts," of an:

electromagnetic reverse braking contactor: lsnav ing anoperating windingIB'iv', a polarizing Wind: s. Hm and a n rm lly-open control circuitcontact me. Preferably the windings I511 lip; I 8w and [8p areintermittent duty windings}.

Before the motor' is connected forfoQefa-tioiito a source of directcurrentfrepresentedby'the supply conductors 2| and Z Z thecontactS'Ilia; ltb',v I8a and "lb are'mov'e'dito their open posiftions as aresult of the energizati'onofithe wind ings ifiw and I810. Aslsh'owriinFig; 1, t'h'ei wind? ings i810 and I810 are connectediiri' serieswith'each other acrossthe supply. conductors'lland" 22 upon closure ofsuitablecontrormearis; such:

as n'o'rm'a'lly open contactsizlia and 25aof5a1ow; voltage protectionrelay 24 anda' braking control relay 25, respectively; and theenergization" or these windings may be increased temporarily whendesired by'momentary closure of a time delay opening" contact 2621. ofa" relay 26. which contact when closed by passes. a protective re sister28 in serieswiththeWindings Ifiw and'itw; With. the; contacts. IBa,I'Sb; we, and I8?) open; the contacts I'Za; I2b, and. I'S'amay be closedto connect the motor for forward runningj'operation' as indicated inFig: 2, or"the' contacts" I ia', I41); and i511 may be closed to connectthe motor'for reverse running" operation" as indicated in Fig; 4. Itisapparentfrom'Figs; 1',, 2:1 and 4 that'the"-di:-- rection ofmagnetization of" the arm'aturawind e i'ng- I0 is reversed while thedirection of magneti zation of the field" winding H remains the same in"order to control selectively the direction'of operation of the motor;

The polarizing winding. I 610" is? arranged to be connectedthrough thecontacts I fic'and thepolarizing winding IBp is arranged" to beconnected through the contacts. I8c; in parallel with each other acrossthe armature winding I0; A resistor 29 is preferably connected inserieswith the windings Hip and I8p'and isnormally by-pass'ed by acontact 30a of. a relay 3!] responsive to the" counter-E. M. F. of themotor.. Thus; after the windings I6w and I8w are energizedto move therespective contactors I6 and l8.to their picked-up positions, the motorcan be started'and the wind? ings Hip and 18p become energized dueto thevoltage drop across the armature winding I'D; Since. the resistor 29is.by-passedby'thecontact and I811 are strongly energized during initialacceleration even though the drop across the armature I0 is low. Therelay 30 responds to open its contact 30a as soon as the motoraccelerates to a predetermined speed, and the protective resistor 29thereby is effectively connected in series with the windings Hip andI813. Preferably the drop-out flux value of the contactors I6 and I8 ismade as low as possible.

When the motor is operating in the forward direction, the direction ofcurrent through the armature I I! is from the terminal Illa to theterminal Iflb and the direction of current through the field winding IIis from the terminal IIa to the terminal I lb as indicated by the dottedarrows in Fig. 2. The direction of current through the windings IGw,I610, I8w, and Iflp for forward operation is as shown by the solidarrows in Fig. 2 which solid arrows also indicate the direction of theflux produced by the respective windings. During forward operation ofthe motor, the windings IBw and I810 assist each other in holding thereverse braking contactor I 8 in its picked-up position, and thewindings IEw and Hip oppose each other. The flux of the winding I620 ismaintained greater than that of the winding IEp so that the algebraicsum of the opposing fluxes is an excess fiux. The windings are sorelated that the excess flux normall is above the drop-out flux of thecontactor I6. Thus the excess flux is sufficient to hold the contactorI6 in its pickedup position.

Upon failure of power or other reason causing one or the other or bothof the contacts 24a or a to move to their open positions, the contactsHo and I2b also open and the windings I611. and I8w become deenergized.As mentioned above, for forward operation, the contacts I611 and I6b areheld in their open positions because of the excess of flux. above thedrop-out value, produced by the winding I6w over that produced by thewinding I610. Although the winding I Sp remains energized in the samedirection for an instant after opening of the contacts I2a and I2b dueto the residual counter-E. M. F. of the armature Ill, the loss of theflux produced by the opposing winding I610 causes the total flux in thecontactor IE to reach zero. At this instant, the contactor I6 drops outand opens its contacts IBc to prevent further energization of thewinding IGp. Drop-out of the contactor I8 also closes the contacts Iliaand IE1: to com lete the dynamic braking circuit of Fig. 3. During theshort interval from the instant power is removed from the armature I0until the dvnam c brakin circuit is established, the windin IBo isenergized by the low counter voltage obtained from the residualmagnetism in the motor field, and the contactor I8 does not drop out.Since the resistor 29 is effectively in series with both windings Hipand I8p during normal running, opening of the contact I60 causes anincrease in the voltage across the winding I811 further insuring thatthe contactor I8 remains in its picked-up position. The direction of theflux of the contactor I8 is not altered and its magnitude is maintainedabove the drop-out value of the contactor I8 until a very low speed isreached. The contact a preferably closes at a predetermined reducedspeed of the motor to short circuit the resistor 29 thereby to cause thevoltage across the winding I8y substantially to equal the countervoltageof the motor during the latter stage of the braking cycle.

As shown by the arrows in Fig. 3, the counter- E. M. F. after forwardrunning causes a dynamic braking current to fiow from terminal IOa ofthe armature I0 through the field winding II from the terminal I la tothe terminal I Ib and through the resistor 20 to the armature terminallab. The direction of current flow through the armature I 8 has reversedbut the current in the field winding II has remained in the samedirection and the motor is brought to rest or to a very slow speed bydynamic braking torque.

When the motor is connected to the supply lines for operation in thereverse direction by closure of the contacts Ma, I lb, and I5a, thedirection of current flow through the armature III is from the terminalIIlb to the terminal Ifla which is opposite from the direction duringforward operation, but the direction of the field current in eachinstance is the same as shown by comparison of Figs. 2 and 4. The solidarrows of Fig. 4 show that during reverse operation the windings IBw andI61) assist each other in holding the contacts I611 and IBb open,whereasthe windings I810 and I811 now oppose each other so as to providean operating excess flux in the same manner as is provided by thewindings Ifip and I Sw when the motor is operating in the forwarddirection. The contacts I8a and I81) remain in their open positionsbecause of the excess flux produced by the winding I8w.

When the motor is rotating in the reverse direction and the contacts 24aor 25a or both open, the contacts I la and Mb also open, and thewindings I6w and IBw become deenergized. The contacts I81: and I'Bbclose because the flux of the contactor I8 reaches zero due to the factthat the windings I8w and Hip are in opposition during reverseoperation. This also causes the contact I8c to open preventing furtherenergization of the winding I8 0 by the generated current of the motorand increasing the voltage across the winding I611. The contacts Mia andIBb remain open due to the energized condition of the winding IBp. Themotor is now connected for dynamic braking as indicated in Fig. 5 withthe armature current flowing from terminals Illa to I81) and the fieldcurrent flowing from terminals II a to III).

A control system in accordance with this invention for graduating orcontrolling in steps the dynamic braking action just described iillustrated in Fig. 6 in which the motor is shown connected in a dynamicbraking loop with the resistor 20 which may be the loop of either Fig. 3or Fig. 5. A section 20a of the resistor 28 is arranged to be by-passedby a normally closed main contact 3Ia of an electromagnetic contactor3|, and a section 202) of the resistor 29 is arranged to be bypassecl bya normally closed main contact 32a of an electromagnetic contactor 32. Athird series-connected section 280 of the resistor 20 may also beprovided. The contactor 32 preferably has an intermittent duty operatingwinding 32w connected across the armature IU through a protectiveresistor 34.- The resistor 34 is arranged to be by-passed by a circuitincluding a normally closed contact 35a of a relay 35 connected inseries with a normally open contact 3Ib of the contactor 3|. The relay35 has an operating winding 35w connected directly across the armature I0. An operating winding 3Iw of the contactor 3| is arranged forenergization from the power lines 2| and 22, and is controlled by abraking master switch 36 having stationary contact segments 36a, 36b,and 360 and a relatively movable contact segment 36d. First, second, and

third positions oithemaster switch at. are provided as indicated by thevertical brokeniines 1,2, and 3, respectively. The segment 36c 03 the.master switch 3.6. may beconnected' to the supply conductor?! through acircuit includin th orm ly pen control conta t 24c or throu h a parallelcircuit inc in a normally closed control contact 39a of a relay 39-andanofi point of a speed controlling master switch 40-havinga plurality ofcontacts 40 through Mornovable with respect to a plurality of segmentsMiq through 492 (Fig. 7). The master switch 40 may be ra P 'Q 6 thr eforward and three reverse speed positions as shown in Fig. 7.

While the motor is at rest as well as during drifting, acceleration, andnormal runningof the motor in either the forward or reverse direction,thecontact 24a is closedso long as power is available. With the brakingmaster 3B in the first position, a circuit is completed for the windingBlw and the contact Eta, is open andthecontact 3th is closed. Thepick-up voltage of the contactor 32 is below that of the relay 35 sothat, during acceleration, the winding 32w issub jected at first tosubstantially the full counter-E. M..F. of the arm tur I thr h a circuiin ludin h co tacts 35c and 31 Wh n h mo or acc le at s to apredetermined low speed, the contactor 32 picksiup a d op nsitscontactsza. Aiu th r increase in speed of the motor causes pickeup ofthe relay 35 due to the operative energization of ts winding 35wr su1tnsfr he in r ased m cratedvoltas of h a ma r 9- Pick -up of the ,relay35 opens .the contact 35a to interrupt the by-pass circuit around theresistor 34. The drop-outvoltage of the contactor 32 with thereesister-.34 effectively in series with the winding SZwisbelow the pick-upvoltage of therelay 35 so that the contactor v32 remains in its operatedpositionwith the protective resistor 34 in series with its winding 32w.

To brake the motor by manual control, the master switch 36 maybe movedto its second position which ,effects completion in a manner to bedescribed of one or the other of thetwo dyenamic braking loops shown inFig. v3and Fig. depending upon the direction of motor rotation. If themotor is running at an appreciable speed, the contactor 32 remains inits picked-up posi tion after the braking circuit has been established.After the motor. has decelerated to a predetermined speed, the relay 35.QI'OPSJOHt and recloses its contact 35a to complete theby-pass circuitaround the resistor 34. With the resistor 34. excluded from its circuitthe winding 321w is connected directly across the armature l0 andthecontactor 32 does not drop out until the motor slows down .to apredetermined speed near standstill, such as, for example, less than oneper cent of rated motor speed. So long as the braking master switch 36is left in the second position, all .of the resistor 28 is eiTective inthe dynamic braking circuit and a constant value of dynamic brakingresistance isobtained down tosubstantially'zero speed.

'gized whenever the contactors 12 or the resistor '34 upon. closureqofthe contact 35,11 which closes when'the motor reaches a, preciseterminedreduced speed. With the resistor 34 effectively connected in series withthe Windin 3220, the contactor 32 drops'out at a motor speed of aboutforty percent instead of less than one per cent as before. Drop-out ofthe contactor 32 causes closure of the contact 32a which icy--v passesthe resistor section 201) leaving onlythe section 200 efiective in thedynamic braking loop and increased braking torque is developedat slowspeeds.

With the motor running in either direction and the master switch 36 inthe first position, a failure of power causes the proper braking cir-.cuitto be completed as described above. :The failure-of power alsocauses closure of the contact aw, due to deenergization of the winding3lw regardless of the position of the master switch 36 and brakingproceeds automatically as when the master 36 is moved to the thirdposition with power still available. During the interval betweentheopening of thecontactors i2 or Id and the build up of dynamic brakingcur-. rent after closure of the selected dynamic braising contactor IE5or i8, the voltage a'crossthe a mature i0 decreas s to a very l wvalu-he.- fore itag ini c e s s du to the dynamic brake ing action, Eventhough the resistor 354 may be ct v y onnect in series withth -wind ins.3220 at thistime, the contactor 32 does not drop out during the shortperiod of reduced voltage drop across the armature because of the closedloop circuit including the armature i0 and the winding321o.

ihus for normal braking operations it is possible for the operator toselect strong or weak braking torque as desired merely by adjustment ofthe master 36. If strong braking is selected, the dynamic brakingresistance is reduced automatically while the motor is still rotating ata substantial speed, whereas, if weal; braking is selected, the dynamicbraking resistance remains constant substantially throughout the brakingcycle. In the event of power failure, strong braking only is obtainedand the graduation of the braking action during deceleration proceedsautomatically.

The directional braking control system of Fig. 1 and the graduatedbraking control system of Fig. 6 may be arranged for cooperativeoperation in a motor control system such as shown in Fig. 7.

Referring to Fig. 7, the forward running'contactor I2 of Fig. 1 is shownas having the main contacts I2a and i219, an operating winding I210, andnormally open control circuit'contacts' I20, l2d, and l2e. The reverserunning contactor [4 has the main contacts Ma and Mb, an operatingwinding'l lw. and normally open control circuit contacts l ic, Md, andie. The contacts I20 and are in parallel with each other between theresistor 28 and the conductor 22 and serve to insure that the windingsI620 and i810 are ener- |4 are picked-up. The negative line contactor l5has the main contact I5a, an operating winding I 5w,

and a normally open control circuit contact (5b.

The acceleration, plugging, and speed control means iii of Fig. 1 may beof any suitable type,

and is shown in Fig. '7 as comprising a resistor sl'having a pluggingsection Ma and an acceleration section Mb. The plugging section Ma isarranged to be short circuited by a main contact 42a of a pluggingcontactcr l Z;-having an operating winding 4210, a normally closedcontrol circuit contact 42b, and a normally open control circuit contact420. A plugging relay of any suitable type may be provided to controlthe operation of the plugging contactor 42 in a wellknown manner. Forillustrative purposes only, a normally closed contact 44a of a pluggingrelay 44 has been shown in Fig. 7. Operating means for the relay 44 arewell-known in the art and need not be described. The accelerationsection 4lb is arranged to be short-circuited by main contacts 45a of anelectromagnetic contactor 45 having an operating winding 45w and anormally closed control circuit contact 451). Suitable means (not shown)may be provided to select the time or speed at which the resistorsection 4; is excluded from the circuit during acceleration, andadditional steps of acceleration and speed control may be provided inthe means I9 if desired.

The relay 24 is a low voltage protection relay having an operatingwinding 24w The relay 25 is a braking control relay and has an operatingwinding 2510 and a normally open contact 25b in addition to the normallyopen contact 25a shown in Fig. 1. The time delay relay 26, which ispreferably of the flux decay type, has an operating winding 26w. Thecontact 26a of this relay is delayed in opening as mentioned inconnection with Fig. 1.

The relay 30 has an operating winding 510w arranged for connectionacross the armature l and includes the normally closed contact 30a ofFig. 1 which by-passes the resistor 29. A resistor 46 connected inseries with the winding 30w is normally short-circuited by a normallyclosed contact 39b of the relay 39 which has an operating winding 39w, anormally open contact 390, and the normally closed contact 39a of Fig.6. The winding 39w is connected across the armature l0 through theresistor 41 which is normally by-passed by a normally closed contact3527 of the relay 35.

A contactor 48 having a normally open main contact 48a and an operatingwinding 48w is provided for completin a shunt connection through aresistor 49 around the armature l0. The resistor 49 is a relatively highvalue and serves to provide a slight excitation for the field winding Hwhile the motor is drifting or coasting. This slight excitation isrequired to provide a voltage during drifting for energizing thewindings supplied from the motor armature.

Further understanding of the arrangement and .function of the componentapparatus of Figs. 1,

6, and 7 will be had from the following description of the operation ofFig. '7.

With the master switch 40 in the oil position shown and the motor atrest, an energizing circuit for the winding 2411) of the low voltageprotective relay 24 is completed from the supply conductor 2! throughthe contact 39a, the segments and contacts 40b, 401', 40q, and 40a, aconductor 5|, and the winding 2420 to the supply conductor 22. Uponenergization of the winding 24w the contacts 24a close to connect theconductor 5| directly to the supply conductor 2i thereby to hold thecontacts 24a closed and the conductor 5| energized irrespective of theposition of the master switch 40.

Upon energization of the conductor 5i an energizing circuit for thewinding 26212 of the time delay relay 26 is completed from the conductor5! through the normally closed contacts Hid and l8d in parallel and thewinding 26w to the conductor 22. The contacts 26a close instantly uponenergization of the winding 26112 to by-pass the protective resistor 28in the energizing circuit for the windings [6w and IBw. With the brakingmaster switch 36 in the first position as shown, an energizing circuitis also completed at this time for the winding 25w of the brakingcontrol relay 25 from the conductor 5 i and the segments Sta, 36d, and36b through the winding 25w to the conductor 22.

Energization of the winding 25w causes closure of the contacts 25a whichcomplete an energizing circuit for the windings 16w and 1820 from theconductor 51 through the windings 16w and i810, and the contacts 26a and25a to the conductor 22. Upon energization of the windings I 610 and18w, the contacts lfia, [6b, 18a and 18b open to interrupt the dynamicbraking circuits and the contacts 16d and [8d open to interrupt theenergizing circuit for the winding 26w. After a short time delay, thecontacts 26a open and insert the protective resistor 23 into theenergizing circuit for the windings lGw and H310.

With the braking master 36 in the first position a circuit is alsocompleted from the conductor 5| through the segments 36a, 3601, and 360,and the winding 3lw to the conductor 22. Upon energization of itswinding 3lw, the contactor 3| opens its contacts 3la and closes itscontacts 3 lb as described hereinbefore.

If it is desired to rotate the motor in the forward direction, themaster switch 40 may be moved to the forward positions to complete acircuit from the now energized segment 401' to the segment 4011, thecontact 49c, and the winding lEw to the conductor 22. Energization ofthe winding i 520 causes closure of the contacts |5a to connect themotor to the supply conductor 22. A circuit is also completed in theforward positions from the energized contact 406 through the winding 48wand the contacts 45b when those contacts are closed. Energization of thewinding 4820 causes closure of the contacts 48a to complete the armatureshunt circuit through the resistor 49. Another energizing circuitcompleted in the forward positions of the master switch is from thesegment 46s through the contact 480, the winding i220 and the now closedcontacts Hie, Mia, and 25b to the conductor 22. The contacts i2a and |2bclose upon energization of the winding [2w to connect the motor to theconductor 2| for forward rotation as indicated in Fig. 2.

If the motor is starting from rest, the plugging relay contacts 44aremain closed, and, as soon as the master 40 reaches the second forwardposition a circuit for the winding 4210 is completed from the segment40a: and the contact 40 through the now-closed contacts [20 and 15b tothe conductor 22. Energization of the winding 42w causes closure of thecontacts 42a which bypass the plugging resistor section 4m to increasethe voltage applied to the motor.

Movement of the master 40 to the third forward position completes acircuit for the winding 4520 through the segment 402, the contact 40g,and the now-closed contacts 420. Closure of the contacts 45a resultingfrom the energization of the winding 45w by-passes the accelerationresistor section M2) to apply full voltage to the motor, and opening ofthe contacts 45b effects the deenergization of the winding 4810. Upondeenergization of the winding 48w, the contact 48a opens to remove thearmature shunt connec- '11 tion through the resistor149. The motornowac- -=celerates to its normalrunning speed.

Acceleration of the motor from rest inithe rea verse direction-isaccomplished in a similar manner except that the contactor l4is-operated in- -:stead of the contactor l2 and the segments 4%,4016,4971], and 4011 serve to complete selectively thecontrol circuitsfor the contactors I4, [5 and A8, 42, and 45.

Reference is now made to the operation, during acceleration, of thecounter-E. M. F. energized relaysand contactors. .As the motor starts torotate, the .-relay30 is the first to pick-up. Openingoi thenormally-closed contact 39a of thisrelay'causes-the resistor 29 to beefiectively inseries with the polarizing windings Hip and 18p. Theresistorlsvnot-only protects the windings tfip .an"d l pthermally but.also limits the flux of these windings to a valuebelow the. fluxprovided by the windings ifiwand [8w to prevent dropping out ofwhichever one of the contactors I6 or 18 .has'its windings in oppositionat the time. The resistor 29 affords this protection so long as thevoltage across the armatureis below the supply voltage. During plugging,however, the voltage acrossthe armature risesabove the supply voltage.and additional means are provided to insure proper operationunder thiscondition as .hereinaiterdescribed.

Since the relay 3!] picks-up at a very low voltage, it has anintermittent duty winding which requires protection against the highervalues of counter-E. M. 'F. Thisprote'c'tion is provided by'the'resistor 45 which isiefiectively inserted in series with thewinding 30w by opening of the contact 391). 'The relay.39'has a'higherpick-up "value than'the' relay 30 and'picks'up later during accelerationto open the contact 3%. Pickup of the relay 39 also opens thecontact 39aand 'closes the contact 390. Closure of the contact 390 completes acircuit from the conductor 5! for *the windings l5 and 48whichis'independent of the master switch 40. "Thus, upon return of themaster switch 4ll-toits off position, the contacts 15a and 48a remainclosed solong as the motor has a sufficient counter-3 M. F. to maintainthe relay.1;39 Lin its ;.picked=-up position. With the contacts 5a and48a closed and the motor: otherwise ,disconnectedfrom the source, thereis sufficient excitation of the field winding H to maintain the1counter-E.-Mi.F. operated contactors and relays in their picked-up,positions thus permitting the motor to drift.

Acceleration of the motor also causes pick-up of the contactor 32 andthe relay as described ,hereinbefore. Pick-up of thecontactor32 opensthe'contact 32a to remove the short circuit from the resistor sectionZUband pick-up of the relay 35 opens'the contact 35a to' insert theresistor 34 in series withthe winding 32w and opens the contact 35b toinsert the protective resistance in series with the winding 39w.

' If the motor is operating in either'the forward or reverse directionsand the'operator desires'to allow the motor to coast, the master 40 isreturned to the ofi position. This causes the-contactors l2 or M, 42 andto drop"out,'but'the contactors l5, l6, i=8, -3l, 32,-and 4syremain intheir picked-up positions. Drop out of the contactors l2 or Mdisconnects the armature I 0 from the supply conductors. The'windings15w and 48212 are maintained energized so long as the motor is rotatingat a substantial speed by'a circuit from the conductor 5| through theconitacts 39c. Thefield winding ll remains energized through .thecontacts 48a, .thei resistors :49

iand-4 I ;'-and:-the :contacts +511 tozmaintainia zgenaerated voltage oflow *value: across :the arma- -:ture lil. =-If,-'at'any time whilethemotor isrotatingyit .is desired toconnectthe motor for weak dynamicbraking, the braking-master 36 may be operated thefirstbraking-position. This interrupts the :oircuit to the winding-25w toeffect-opening .of :the contacts 25a and 25b. Opening of thesconta'cts25b interrupts the circuit for. the-windings :I-Zwor 14w effectingopening of the contacts 12a and 12b or Ida and 14b. Opening-'of thecontacts:25wdeenergizes the windings :l'sweand 18w :and ?-the contactors1 I Sand i8'athereaiter respond :in accordance with the descriptioniof.Figs.-:3,and :5. :Further braking *operation may proceed'as describedin connection With-Fig. .-6.

During plugging, the voltage-across the armature lfl canincr-ease to a.value :suchthatthere would be a tendency for the winding Hip or-l8p:which was opposing the corresponding :winding "I'Bwor l8w at the timeto overpower-its corre- ';sponding winding. To prevent this,.a 'circuitis .:provided for the windingiitw from the conductor :5 i throughthe-contacts lid and ii' idin, parallel, :the contact 42b, and thewinding "2 fiw to'the con- -ductor 22. -When the master .40 is movedthrough the first and off positions for plugging, thecontact i i-2b.closes and completes the :above described circuit through eitherthe'contact'liw: or Add. As soon as the motor reverses, the. contact5421) reopens. ."However.thewindingflfiw has-been energizedmomentarilyand the contact 2Gaicloses and-remains closed-for;a'predetermined timeduring plugging. Closure of the :contact -2 6a in- :creases theenergization of the windings i fiw'and mew-by bypassing the resistor28.

,If. braking operationis initiated by a failure of .power, it isdesirablethat braking be continued -and:the motor brou-ghttoresteventhough power returngduring the braking interval. ."In order .to preventresetting 'ofthe low voltage: protective relay 24 while the motor isrotating-the contacts 355a are interposed in the circuit leading to themaster 4B. The contacts 3a remain open during braking andpreventtreenergization :of the relay 24.

We claim: H

l. In a controller and motorcombinatiom a .direct current motor arrangedfor connection .to asource of power, anarmature circuit including thearmature'winding of themotor an electromagnetic switchhaving itscontacts .in said circuit andv having a pairof windingsfand a magneticcircuit at .-least:a: portion of vwhich is common to saidwindings,relectrical:connections respective to said windings. forenergizing said windings in oppositiontoeach.otheriso that the fluxproduced in said .commonportion by one. of said windings is normallyin-excessof the amount of fiuxproduced in said common portion by theotherof said windings andvsaid excess is normally above the drop-outflux value of said switch, one of. said electrical connectionsconnecting said one winding to a power source for the motor theother ofsaid .electricalconnections connecting said other winding in shuntrelation to said armature Winding, said .switch being held inone-position .by-the algebraic sum of said fluxes when said algebraicsumexceeds said drop-out valueandbeing operative to move to anotherposition upon reduction .of the algebraic sum of said fluxes below saiddrop-out value, and means operatively'in said one :electrical connectionand. responsive to..a..failure .of

voltage of said source for reducing the flux of its respective windingso that the algebraic sum of said fluxes is below said predeterminedamount.

2. The combination of claim 1 characterized in that means are providedfor plugging said motor and in that means are provided for increasingtemporarily, when said motor is plugged, the voltage applied to said oneof said windings.

3. A controller comprising an electromagnetic switch having its contactsadapted to be connected in a circuit with the armature winding of adirect current motor and having a pair of windings and a magneticcircuit at least a portion of which is common to said windings,electrical connections respective to said windings, one of saidelectrical connections being adapted to connect its respective windingto a power source for the motor, the other of said electricalconnections being adapted to connect its respective winding in shuntrelation to said armature winding, said windings being adapted to beenergized in opposition to each other when said electrical connectionsare connected to the power source for the motor and in shunt relation tothe armature winding respectively so that while the motor is rotating inthe direction of its torque the flux produced in said common portion byone of said windings is in excess of the amount of flux produced in saidcommon portion by the other of said windings, and said excess isnormally above the drop-out flux value of said switch so that saidswitch is held, when said electrical connections are so connected forproducing said excess of flux, in one position by the algebraic sum ofsaid fluxes and is operative to move to another position upon reductionof the algebraic sum of said fluxes below said dropout flux value, andmeans operatively in said one electrical connection and adapted to beresponsive to a failure of voltage of said source, when said one of theelectrical connections is connected to said source, for reducing theflux of its respective winding so that the algebraic sum of said fluxesis below said drop-out flux value.

4. A motor and controller combination comprising a direct current motorhaving a series field winding, means for supplying an operating voltageto said motor, a dynamic braking circuit for said motor including saidfield winding, a normally-closed electromagnetic switch in said dynamiccircuit for controlling the continuity thereof and having a pair ofwindings and a magnetic circuit at least a portion of which is common tosaid windings, electrical connections respective to said windings forenergizing said windings in opposition to each other so that the fluxproduced in said common portion by one of said windings is normally inexcess of the amount of flux produced in said common portion by theother of said windings and said excess is normally above a predeterminedamount, the electrical connection for said other of said windingsconnecting said other of said windings in shunt relation to saidarmature winding, said switch being held in its open position by thealgebraic sum of said fluxes when said algebraic sum exceeds saidpredetermined amount and being operative to move to its closed positionupon reduction of the algebraic sum of said fluxes below saidpredetermined amount, and said electrical connections for said one ofsaid windings including means rendering the amount of flux produced insaid common portion by said one 14 of said'windings directly dependentupon the amount of voltage supplied to said motor.

5. In a controller for an electric motor, means for connecting the motorto a source of power for rotation in opposite directions selectively, apair of electromagnetic switches, a first pair of windings for operatingone of said switches and a second pair of windings for operating theother of said switches, electrical connections for supplying one windingof each pair of said windings with an energizing voltage dependent uponthe voltage applied to the motor, said one winding of each pair ofwindings being operative when supplied with said energizing voltage tohold the switch associated therewith in one position, and electricalconnections for supplying the other winding of each pair of windingswith a voltage the magnitude of which varies with the speed of the motorand the polarity of which depends upon the direction of motor rotation,and one of said pairs of windings being in opposition for one directionof motor rotation and being additive for the other direction of motorrotation and the other pair of windings being additive for said onedirection of motor rotation and in opposition for said other directionof motor rotation.

6. In a controller and motor combination, a direct current motor havingan armature Wind'- ing and a series field winding, means for connectingthe motor to a source of power for forward and reverse operationselectively, a first normally-closed electromagnetic switch means whichwhen closed connects the motor windings in a closed loop circuit fordynamic braking while the motor is rotating in the forward direction, asecond normally-closed electromagnetic switch means which when closedconnects the motor windings in a closed loop circuit for dynamic brakingwhile the motor is rotating in the reverse direction, each of saidswitch means having a pair of windings and a magnetic circuit at least aportion of which is common to its pair of windings, means for connectingone winding of each pair for energization from said source of power,means connecting the other winding of each pair to the motor forenergization by the generated voltage of said motor, the pair ofwindings assoelated with the first normally-closed switch means being inopposition while the motor is rotating in the forward direction andadditive while the motor is rotating in the reverse direction, the pairof windings associated with the second normally-closed switch meansbeing in opposition while the motor is operating in the reversedirection and additive while the motor is operating in the forwarddirection, the flux produced in the common portion of the associatedmagnetic circuit by said one winding of each pair being in excess of theamount of flux produced in the common portion by the respective otherwinding of each pair, and each of said switch means being held in anormally-open position by the algebraic sum of the flux in the commonportion of the magnetic circuit thereof and being movable to itsnormally-closed position upon reduction of said algebraic sum below agiven value.

7. A controller for a direct current motor havingan armature winding anda series field winding, means adapted, when connected to said motor, toconnect the motor to a source of power for forward and reverse operationselectively, a first normally-closed electromagnetic switch ineansa'dapted to connect the motor windings fawn-goat $13 :in az'closediloopcircuitifondynamic brakin'g while the motor is rotating in ''-theior-ward direotion, a second -nlfllal1Y-01OSBd electromagnetic swi-tch.meansadapted to connect'the motor win'dings in la closedloop circuitfor dynamic braking while the motor is :rotating in the reverse:direction, each of said switch meansincluding-a-pair of windings andamagnetic circuitatleast-a portion of which is common to itspair of-windings, -means cadapted to connect one -winding ofeeach ipair iorzenergizationirom saidsource of power while-the motor is :also connectedto :said "source, r means adapted to :connect :-the :other winding ofeach pairito the motor I for energization by. the generate'd voltage'ofsaid motor, the pair of windings zassociated with the firstnormally-closed switch :means being in 'opposition'while the motorrotating in the forward direction -:and additive while themotoriisoperating"in:the.-reverse directionpthe :pairoi" windingsassociated withthe second .normally-closed switch --means being .in lopposition whilethe motor is operating in the reverse direction and additive while themotor iis operating-in the forward direction, the flux produced in thecommon portion of the associated magnetic circuit by said one winding ofeachpair being in excess of the amount of flux-produced in the :commonportion by the respective other winding of each =-pair, eaoh of said"switch means "being held in-a normally-open position --by thealgebraicsum of the-fluxes in the common por- *tion of: the magneticcircuit thereof and bein movable 'to its "normally-closed position ruponreduction of- =-said algebraic sum below a given A'windingsymagneti-c'meansarrangedto "be sup- :plied'with' an "energizingvoltage which 'varies with the voltage applied to themotor :andoperative -for opening said normally-closed"switches when voltage is;applied to the motor, said magnetic mea-ns including meansforpreventing-"clo- "sure of certain of said normally=closed switcheswhen voltage isremoved'from themotor. afirst normally-closed magneticswitch'meansarrange'd *to be energized from the sourceofpower andoperative upon failure of voltage "of said "source for-commutating aportion of saidresistorfan'd :asecond normally-closedmagneticswitcnmeans arranged to be energized bythe counter voltage ofsaidmotor and operative, consequentpupon a predetermined reduction ofthe countervoltage when some of'said'normally-closedswitches are "closedand saidimotor is rotatingfito commutate another portion of saidresistor.

9. .JA controller :in accordance with "claim *8 characterized inthatsaid controller includes a "manually operated means having twopositions of" movement, means operable when 'said manuallyoperated meansis in one of said two positions for opening said normally-open switchesto remove voltagefrom said motor ,and for interrupting the "supply ofvoltage from said source to said magnetic means-while maintaining'fbothof-'saidmagnetic switch means inoperative until said "motorcomes to"rest, whereby certain ofsaiii normally-closed switches --cl0se' tocomplete one or said dynamic 'braking circuits =an'dwhereby :neitherportion of said resistor is --commutated, and means-'operable-whensaidmanuallyoperated means is moved from said first positionto said :secondposition to permit sequential operation of said magnetic switchmeansbefore said'motor lcomes to 'rest. V

.10. A controllenfor a direct current motor comprising V a dynamicbraking resistor, switching 'means for completing :a dynamic braking pcircuitincludingsaid resistor and the-armature :winding of the motor,magnetically opened icontacts connected .in shunt relation with:seriesconnected iportions-ofi said resistor, respectively, =manualmeans operable for controlling r.-the:clo- .asure :of ;one:of said:contacts, :means mendere'd toperative Soy ;rotation of ithe ;motor for:controliling theclosure of :the other'of saidcontacts :in

accordance ;.with the: motor.- speed while saidloop iCiICIlitliScompletedrand: means dependent'upon 'theeoperative position of .:.saidtone of .said contactsifcr determining .at which.one.;of two. mo-;tonspeeds said means operatesto .efiectsclosure coftheother.ofssaidzcontacts. y

11. ,A controller in accordance with .claim :.10 characterized in thatsaid means rendered ;op- :erative :by rotation i of the vmotor comprisesan operating winding for the other of :said. contacts and inithat saidmeans .dependent upon thexoperative position of said oneofsaidcontactsiinecludesa resistor connected ,iniseries withisaid :winding.

12. Ina controller. and motor combination, a direct currentmotorhavingranyarmature wind- ;ing and o a-series. field winding,reversingswitching means connected to said motor for energizing saidmotor from a:source of powerfor forward .and reverse operationselectively, circuits adaptedto be'completed to form dynamicibrakingloops with the motor windingsrbrake switch means for completing the saidcircuits, said brake switch means including apair of electromagneticswitches each operative in response to the aatlgebraicsum ofapairoffluxes in its magnetic-circuit, said brake switch means havingcooperating flux-producing portions causing the direction of-one-of theifluxesin each ofsaid switches .to be-independent of the direction ofmotor rotationeand the direction of the other one of'the fluxesin eachof said switches to'be dependent upon thev direction of motor rotation,and means connecting said cooperating portions to saidv motor .and tosaidv source so that the fluxes, intone ofsaid switches are opposed forone direction .ofmotor rotation and are additiveforthe other directionof motor rotation, whereas the .fiuxes in the other ofsaid switchesareadditive for said other direction of ,motor rotation and substrac- .tiveforsaid one direction of motor rotation.

13.'In a controller for a direct current motor having an armaturewinding and a series -field winding, reversing. switching means forconnecting said motor to a source of power for'forward and reverseoperation selectively, circuits adapted to be completed .toformdynamicibrakingloops with the motor windings, brake switch means forcompletingthesaid circuits, saidbrake switch means including a pair ofelectromagnetic switches each operativein response to thealgebraic sumof a pair of fluxes inits magnetic .cir-

cuit, said brake switch means having cooperating flux pro'ducingportions causing the 'directiontof one of the'fiuxesiin each of saidswitches tobe independent of the direction of ,motormotation and thedirection of the other one or the ffluxes in:cach-xoi said switches tobedependent uponn the directionpf-motor rotation, and means forconnecting said cooperatingportions to said motor and to said source sothat the fluxes in one of said switches are opposed for one direction ofmotor rotationand are additive for the other direction ofmotor rotation,Whereas the fluxes" in the other of said switches are additive for saidother direction of motorrotation and subtractive for said-one directionof' motor rotation.

14. A motor-and controllereombination'comprising a'direct current motorhaving an arma ture winding and a series field winding, reversingswitching means connected to said motor and operable to completecircuits from a source of power through said motor for causing saidmotor to operate in forwardand reverse directions other winding of eachpair of windings with a voltage the polarity of-which is dependent uponthe direction of motor-rotation, one of said pairs of windings being inopposition for one direction of motor rotation and being additive forthe other direction of motor rotation and the other pair of saidwindings being additive for said one direction of motor rotation and inopposition for said other direction of motor rotation, said one windingof each pair of windings producing in said common portion of itsassociated magnetic circuit a flux in excess of the flux producedtherein by said other winding of each pair of windings so long as thevoltage applied to said motor is above a predetermined value, each ofsaid switches being held in an open position by the algebraic sum ofsaid fluxes in the common portion of its magnetic circuit and beingoperative to move to the normallyclosed position upon reduction of thealgebraic sum of said fiuxes in the common portion of its magneticcircuit below said predetermined amount.

15. In a dynamic braking controller for a direct current motor having anarmature and a series field winding, means for connecting said motor toa source of voltage for forward and reverse operation selectively, adynamic braking resistor, an electromagnetic switch havingnormally-closed contacts connected to said resistor and arranged whenclosed to connect said resistor in a loop circuit with said armature andfield windings and having a pair of operating windings and a magneticcircuit at least a portion of which is common to said operatingwindings, connections for one of said operating windings arranged toconnect said one operatin winding to a source of voltage of fixedpolarity the continuity of which is dependent upon the continuity of thevoltage supplied to the motor, connections for the other of saidoperating windings arranged to connect said other operating winding to asource of voltage the polarity of which is dependent upon the directionof rotation of the motor and the magnitude of which is di. rectlydependent upon the speed of the motor, whereby said operating windingswhen connected to their respective voltage sources are additive or'inopposition depending upon the direction of rotationof said motor,said-operating windings being so related to each other that-the-fluxproducedin'said magneticcircuit-by said one operatingwinding is greaterthan the flux produced insaid: magnetic circuit-by said other operatingwinding :'when the motor 'is at its maximum speed, whereby an excess offlux equal to the algebraic sum of said fluxes is produced in saidcommon-portionof said magnetic circuit when said windings-are energizedin opposition, said relatedoperating windings being also so related tosaidswitch that said excess of flux is above the-drop-out flux-value ofsaid'switch; whereby said: switch is held in open position by saidexcessof-flux and-is operative to move to its closed position-:uponreduction of the algebraic sum of said fluxesbelow said drop-out flux.Value, and means for discontinuing thesupply of voltage to said motorand tosaid one winding concurrently,

whereby'the'algebraic sum of said fluxes in said common portion becomeszero before it increases at opposite polarity dueto continuedenergization of said other-winding.

16.-A controller comprising the following fixed combination ofcontroller elements both connected-together and related incharacteristics to eachother so that the fixed combination of theelements can be connected to a direct current dmotor havingan armaturewinding and a series field winding to provide the following combination:a direct current 'motorhaving an armature winding and a series fieldwinding, means for connecting the motor to a source of power for forwardand reverse operation selectively, a first normally-closedelectromagnetic switch means which when closed connects the motorwindings in a closed loop circuit for dynamic braking while the motor isrotating in the forward direction, a second normally-closedelectromagnetic switch means which when closed connects the motorwindings in a closed loop circuit for dynamic braking while the motor isrotating in the reverse direction, each of said switch means having apair of windings and a magnetic circuit at least a portion of which iscommon to its pair of windings, means for connecting one winding of eachpair for energization from said source of power, means connecting theother winding of each pair to the motor for energization by thegenerated voltage of said motor, the pair of windings associated withthe first normallyclosed switch means being in opposition while themotor is rotating in the forward direction and additive while the motoris rotating in the reverse direction, the pair of windings associatedwith the second normally-closed switch means being in opposition whilethe motor is operating in the reverse direction and additive while themotor is operating in the forward direction, the flux produced in thecommon portion of the associated magnetic circuit by said one winding ofeach pair being in excess of the amount of flux produced in the commonportion by the respective other winding of each pair, and each of saidswitch means being held in a normallyopen position by the algebraic sumof the flux in the common portion of the magnetic circuit thereof andbeing movable to its normally-closed circuit with a dynamic brakingresistor, a pair 19 v of normally-closed contacts operative when closedto shunt'respective serially connected portions of' saidresistor,magnetic means respective to said contacts and operative when energizedto hold said contacts open, control means operative to maintain both ofsaid magnetic means energized at the instant of completion of said loopcircuit, said control means including manual means operable at all timesto disable one of said magnetic means while maintaining the othermagnetic means energized thereby to permit the closing of only one ofsaid contacts, and said magnetic means which maintains the other of saidcontacts open including a winding connected to said motor soas to beenergized by the counter-voltage of the motor and be responsive to thespeed of the motor for maintaining said other contact open until 'saidmotor reaches a predetermined speed.

18. A controller in accordance with claim 7 characterized in that meansassociated with the other winding of each pair of windings is responsiveto the speed of the motor for reducing the voltage applied to said otherwindings after a predetermined increased speed has been reached by themotor. r r

19. A controller in accordance with claim 7 characterized in that theother winding of each pair of windings are connected in" parallel witheach other and in series with a common resistor, normally-open contactmeans associated with the first switch means are connected in 20 serieswith the other winding of thefirst switch means and in parallel with theother winding of the second switch means, and normally-open contactmeans associated with the second switch means are connected in serieswith the other winding of the second switch means and in parallel withthe other winding of the first switch means.

20. A controller in accordance with claim 10 characterized in that saidmeans for controlling the closure of the other of said contactscomprises a magnet winding arranged to be connected across the armatureof said motor through a resistor arranged to be by-passed by auxiliarycontacts which are closed when said one of said contacts is open and.which are open when said one of said contacts are closed.

JOHN D. LEITCH. PAUL G. WHITE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,400,077 Keith Dec. 13, 19211,455,668 Scheer May 15, 1923 1,497,780 Gazda June 17, 1924 1,805,248King May 12, 1931 1,839,559 Jenks Jan. 5, 1932

